The present invention relates to the control and monitoring of power systems. More specifically the present invention relates to secure access to a current sensing intelligent electronic device capable of performing multiple power system related functions.
Presently power systems are often controlled and protected by individual protective relays. Each relay generally protects a portion of the power system generally referred to as a zone. The settings of the protective relays are fixed after being configured during the commissioning of the power system. The settings may be input into the protective relays manually through the front panel of the protective relay or via a communications link in which case the person commissioning the system inputs the settings via a terminal or other similar interface. Once the protective relays are setup, the settings are generally not changed or if they are changed, the new settings are once again manually input.
Protective relays sometimes have an output trip signal indication that can be provided to an upstream relay to indicate that a fault has been sensed. The upstream relay may implement a hold off delay before tripping an associated breaker when this signal is received. This signal can be a dedicated digital signal or may be implemented in a communications protocol, but is generally limited to indicating an impending trip of a downstream breaker.
Protective relays often implement some power metering or monitoring functions. Such functions include the monitoring of voltage, current, power, frequency, power factor, energy, etc. Due to the fact that the protective relay may have a wide amplitude range and a narrow frequency response, the measurement accuracy is generally not as high as power meters dedicated to metering and/or monitoring.
Protective relays are generally unable to perform most power quality functions due to their limited measurement bandwidth. Power quality functions include the measurement of the harmonics of the power system frequency present in the voltage and current, power harmonics, symmetrical components, detection of sags, transients and surges, waveform captures, etc.
A consultant study is typically only done once every 10 to 15 years for a power distribution system. At the time of the consultant study, the appropriate settings for each protective relay and other related devices are determined. As the power distribution system changes and/or loads are added or changed, it typically becomes difficult to correlate the information from the last consultant study with the actual operational information of the system during use.